Water soluble polymers such as poly(N-vinylamides), frequently require high molecular weight to develop satisfactory properties for high performance applications. Low to medium molecular weight poly(N-vinylformamide) and poly(N-vinylacetamide) have been prepared by conventional solution polymerization in water and alcohols using oil-soluble and water-soluble initators. However, poly(N-vinylamides) of high molecular weight are difficult to produce by conventional solution polymerization in that the polymer product obtained under useful conditions is a gel which is difficult to handle. In addition, problems with high solution viscosity and poor heat transfer make such synthesis impractical on a commercial scale.
Nonetheless, it was believed by the present inventors that the applications performance of poly(vinylamides) and poly(vinylamines) could be enhanced by the preparation and use of homopolymers of very high molecular weight (&gt;10.sup.6).
U.S. Pat. No. 4,500,437 discloses acrylamide copolymers and terpolymers containing N-vinylformamide and N-vinylacetamide prepared by inverse emulsion polymerization in Examples 67-70 with the polymers of Examples 68 and 70 having a molecular weight below 100,000; i.e. &lt;10.sup.5. Example 20 shows the preparation of poly(vinylformamide) by solution polymerization.
U.S. Pat. No. 4,421,602 discloses linear basic polymers containing from 90 to 10 mole % of copolymerized vinylamine units and from 10 to 90 mole % of copolymerized N-vinylformamide units. This patent teaches that the polymers can be prepared by solution polymerization in water, a water-soluble solvent or a mixture of water and a water-soluble solvent and actually shows such solution polymerization in the examples. It is suggested that the polymerization can also be carried out as a water-in-oil emulsion polymerization in a water-immiscible solvent, but there are no examples of such polymerization.
U.S. Pat. No. 4,018,826 discloses the preparation of poly(vinylamine) salts of mineral acids by polymerizing vinylacetamide with a free radical polymerization catalyst, and hydrolyzing the poly(vinylacetamide) to the desired amine salts by contacting the poly(vinylacetamide) with an aqueous solution of the corresponding mineral acid. Poly(vinylamine) product of about 3,000 to about 700,000 molecular weight (4,000 to about 1,000,000 for the salt product) is suggested.
U.S. Pat. No. 3,558,581 discloses homo- and copolymers of N-vinyl-N-methylamine by hydrolysis of the corresponding polymers of N-vinyl-N-methylformamide with mineral acids.
U.S. Pat. No. 3,597,314 discloses a water-soluble polymer consisting essentially of units derived from N-vinyl-N-methylformamide having 60-100% of the formic acid radicals of the polymer split off by acid hydrolysis. There is no disclosure regarding inverse emulsion polymerization.
GB 2,152,929 is directed to a process for producing N-substituted formamides for use in producing N-vinylformamide by thermally decomposing N-(alpha-alkoxyethyl)formamide in the gas phase. It is suggested that the N-vinylformamide can be bulk polymerized, solution polymerized using an aqueous solution or an organic solution, or emulsion polymerized singly or together with a monomer used conventionally for producing water-soluble polymers suitable for making flocculants, in the presence of a polymerization initiator of azo compounds. The thus obtained poly(vinylformamide) is hydrolyzed under acidic or basic conditions to obtain a cationic polymer of poly(vinylamines).
D. J. Dawson, et al., "Poly(vinylamine hydrochloride). Synthesis and Utilization for the Preparation of Water-Soluble Polymeric Dyes," J. Am. Chem. Soc., 98:19, 5996 (1976) discloses the preparation of N-vinylacetamide and its polymerization in solution followed by acid hydrolysis to poly(N-vinylamine hydrochloride).
Representative of the numerous prior art references relating to water-in-oil emulsion polymerization of water-soluble monomers are the following patents: U.S. Pat. Nos. 2,982,749; 3,278,506; 3,284,393; 3,957,739; 3,975,341; 4,078,133; and 4,312,969.
Perhaps most importantly, R. H. Summerville, et al., "Synthesis of N-vinyl Acetamide and Preparation of Some Polymers and Copolymers," Polym. Reprints, 24, 12 (1983) discloses that the inverse emulsion polymerization of N-vinylacetamide initiated by sodium persulfate in water and cyclohexane using Igepal surfactants was tried without success.